1. Field of the Invention
This invention relates to continuous processes using wiped-surface reactors for free radical graft polymerization of polyolefins, and to graft copolymers thereby produced. In another aspect, this invention relates to polyfluoropolyethers and copolymers thereof. In yet another aspect, this invention relates to polyfluoropolyether peroxides.
2. Description of the Related Art
Processing and/or production of polymeric resins using wiped-surface reactors such as screw extruders and twin-screw extruders is well known (such processing is often called reactive extrusion). Twin-screw extruders and their use in continuous processes such as graft polymerization, alloying, bulk polymerization of vinyl monomers, and condensation and addition reactions are generally described in Plastics Compounding, Jan./Feb. 1986, pp. 44-53 (Else et al) and Plastics Compounding, Sept./Oct. 1986, pp. 24-39 (Frund et al.). Graft reactions are said to be carried out by first melting a polymeric species in the initial stages of an extruder, injecting a peroxide catalyst into the extruder, and mixing in a monomer under high shear conditions. Advantages of the twin-screw extrusion process are said to include narrow distribution of molecular weight, improved melt-flow properties, consistent process control, and continuous processing.
Graft polymerization reactions of polyolefins with various monomers using wiped-surface reactors are known. Such grafting is said to be useful in providing a polymer adduct with functionality to allow further modification of structure and properties. General mechanistic proposals regarding formation of these "mechanochemically synthesized" adducts are discussed in connection with grafting of maleic anhydride onto polypropylene in Polymer Prep., 1986, 27, 89 (A1-Malaika).
A number of particular free radical graft polymerization reactions have been reported. For example, U.S. Pat. No. 3,177,270 (Jones et al.) discloses a process for preparing graft copolymers by mixing an olefin polymer at a temperature between 110.degree. C. and 250.degree. C. while contacting the polymer with a minor proportion of a mixture comprising a monovinyl aromatic compound and optionally one or more other monomers such as acrylic acid, methacrylic acid, acrylonitrile, methyl methacrylate, methacrylonitrile, or maleic anhydride, the mixture having dissolved therein an organic peroxide.
British Pat. No. 1,292,693 (Steinkamp et al.) discloses use of a single-screw extruder to graft monomers such as maleic anhydride and acrylic acid onto polyolefins such as polypropylene in the presence of a suitable free radical initiator such as an organic peroxide. The product graft copolymers are said to have a melt flow rate (MFR) of at least 50% greater than the MFR of the base polymer.
U.S. Pat No. 4,003,874 (Ide et al.) discloses modified polyolefins obtained by adding an unsaturated carboxylic acid or an anhydride thereof and an organic peroxide to a polyolefin and melting these components in an extruder. The polyolefin so obtained is said to adhere to glass fibers.
U.S. Pat. No. 4,146,529 (Yamamoto et al.) discloses a process for production of modified polyolefins by combining a polyolefin with one or more carboxylic acids or their anhydrides in an extruder in the presence of a radical producing agent and an organosilane.
U.S. Pat. No. 4,228,255 (Fujimoto et al.) discloses a method for crosslinking a polyolefin, the polyolefin being a low density polyethylene or a polyolefin mixture containing a low density polyethylene, comprising reacting the polyolefin with an organic silane and an organic free radical initiator to form a silane-grafted polyolefin, then mixing the silane-grafted polyolefin with a silanol condensation catalyst. The mixture is extruded with heating in a single-screw extruder to provide a crosslinked polyethylene.
U.S. Pat. No. 4,857,254 (Wong et al.) discloses a method of grafting styrene and maleic anhydride to molten hydrocarbons in the absence of an initiator.
Complex polyfluoropolyether peroxides can be made by photooxidations as described in U.S. Pat. No. 4,743,300 (Brinduse et al.). Also described therein are functional polyfluoropolyether derivatives such as polyfluoropolyether acrylates, and the free radical polymerization of such derivatives. The polymerized materials are said to have useful properties such as low coefficient of friction, high resistance to chemicals, high oxygen permeability, and thermal stability over a wide range of temperatures.
U.S. Pat. No. 4,085,137 (Mitsch et al.) discloses polyfunctional poly(perfluoroalkylene oxide) compounds, such as compounds of the formula ##STR1## where A and A' are reactive moieties containing a polymerizable functional group, e.g., a polymerizable double bond. Such compounds are said to be useful as monomers in the preparation of polymeric materials possessing unusual low temperature stability and resistance to solvents.
Also known are less complex polyfluoropolyether peroxides, prepared by the photochemical reaction of oxygen with: tetrafluoroethylene [U.S. Pat. No. 3,715,378 (Sianesi et al.)]; hexafluoropropylene [U.S. Pat. Nos. 3,699,145 and 3,896,167 (Sianesi et al.)]; mixtures of one or more perfluoroolefins [U.S. Pat. Nos. 3,442,942 (Sianesi et al.) and 3,450,611 (Loffelholz et al.)]; or perfluorodienes [U.S. Pat. No. 3,451,907 (Sianesi et al.)].